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Registered Member #1822
Joined: Fri Nov 21 2008, 08:04PM
Location:
Posts: 300
Can extreme low pressure pumps handle moisture? I wanted to try and cook some stuff at very low pressures and tempuratures since I saw a device that does that and costs a couple grand.
Registered Member #135
Joined: Sat Feb 11 2006, 12:06AM
Location: Anywhere is fine
Posts: 1735
No. The moisture is a contaminant in the oil and also becomes a vapor in your vacuum system preventing it from achieving high vacuum. Moisture needs to be isolated from the system by trapping it either in an absorbant or cryo-trap.
Even roughing pumps are at a certian level of risk when it comes to moisture. Moisture corrodes the housing at a slow pace, but the worst part is you cannot achieve high vacuum, so you have to dump a quart of oil.. ~ $30.
Registered Member #1451
Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661
Normal food won't stand up to a good vacuum. It would most likely vaporize because of the pressure. I bet that device you saw cook saw cooks the food at a low pressure for human, say 1/2 atmospheric pressure. Might even be done with a fridge compressor used in reverse. Even at that pressure the boiling point of water is decreased to something close to room temp. I don't know how those pumps like moisture, but they're found everywhere so you might try it and not be devastated if you ruin the pump.
Registered Member #2123
Joined: Sat May 16 2009, 03:10AM
Location: Bend, Oregon
Posts: 312
Stainless steel body rotary vane pumps can pump moisture. In the Semicon Mfg industry these pumps handle all kinds of nasties, like HCl gas. The water content may build up in the pump oil, affecting base pressure, but there are pump oils with very low affinity for water. If you want to get fancy you can re-circulate the oil through a dessicant and filter to remove impurities.
Registered Member #53
Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638
Fridge compressors used a vacuum pumps will stand up to A LOT of abuse ;), they lower the boiling point of water to about 60-70degrees C (mine does anyway). The only problem is the oil in them goes rotten or something after a while and it smells terrible (still pulls a vacuum though).
Registered Member #1134
Joined: Tue Nov 20 2007, 04:39PM
Location: Bonnie Scotland
Posts: 351
Remember, that common or garden 'fridge pumps, have the lower portions of the motor windings very close to, if not submerged in, oil at the bottom of the pump. Any significant ingress of water, may cause a short.
As Nik said, they are very hardy, and dirt cheap. Still I would be inclined to devise some sort of trap for the water vapour.
Registered Member #53
Joined: Thu Feb 09 2006, 04:31AM
Location: Ontario, Canada
Posts: 638
I for got to mention that when there is any moisture in the container it does a terrible job at evacuating it. The water will just boil and bubble for minutes until it has all become a vapor. Fridge pumps only have mediocre throughput (volume per time)
Registered Member #1643
Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039
Anyone ever reverse engineer a tire pump? I see those can be hacked for vacuum. I just wondered how much, and if you could use it for transformer oils also.
Registered Member #1822
Joined: Fri Nov 21 2008, 08:04PM
Location:
Posts: 300
.5 ATM should be really easy to achieve! I will just wait for someone to throw out a fridge and take the pump then.
Hypotheticly if someone were to have utter disregard for the laws the EPA has set in place and cut the freon line to discharge it would they be in any physical danger from high pressure discharge, low temperatures or inhalation?
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Vacuum Pump
